In nuclear waste repository design bentonite has been included as part of the backfill for its sorbtive capacity and low water permeability. Nevertheless, it cannot keep the waste form dry once intrusion of groundwater has occured [1]. Leach experiments [2], [3] with the radioactive nuclear waste form borosilicate glass JSS-A have been performed with and without bentonite present to provide a database which allows the long term stability of the glass in aqueous environment to be forecasted and the chemical effects of bentonite to be studied.

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This article reviews the electropotential relation between the internal Ag∕AgCl reference electrode used in nuclear light water reactor (LWR) applications and the standard hydrogen electrode (SHE). The focus is on the formation of AgnormalCln1−n complexes and how these might affect the potential of the Ag∕AgCl electrode. In LWR applications the internal Ag∕AgCl reference electrode is subjected to temperatures up to above 300°C , depending on reactor design. At temperatures of 150°C , the solubility products governing the concentration of AgnormalCln1−n complexes and thus the concentration of free Cl− in solution are different from what is known at room-temperature conditions. The potential of the Ag∕AgCl electrode is in turn dependent on the concentration of free Cl− . Therefore, it is likely that also the potential of the reference electrode is altered, compared to the value derived by ignoring the formation of AgnormalCln1−n complexes. The review is based partially on data from literature and partially on thermodynamic calculations. Thermodynamical calculations based on the revised Helgeson–Kirkham–Flowers model were used to derive the equilibrium concentration of free Cl− . The revised electropotential relation between the internal Ag∕AgCl reference electrode and the SHE assigns the electrode a higher potential compared to currently used models.

Two types of simulated nuclear waste glasses were leached and simultaneously gamma-irradiated. The leachate pH was reduced through irradiation, which enhanced glass leaching at room temperature. In contrast, the pH was maintained almost neutral in the experiment at 90°C and the leach rates were about five times lower than those for the glass leached at 90°C but out of the radiation field. Most of the leach rates correlated with the final pH of the leachate. Ground water, granite and bentonite moderates the effect of gammairradiation, probably because of a buffering effect. Simultaneous weathering and irradiation could greatly change the surface morphology of the glass.

The corrosion experiments of crushed, radioactive waste glass at Studsvik within phase V of the JSS Project are described. The experiments were performed with high S/V ratios (1100 and 4000 m−1) which resulted in silica saturation already after the shortest reaction time studied (91 d).Thee long term leach rate of the soluble elements is about 10−3 g.m d−1, both in the presence and absence of bentonite. In the presence of bentonite + magnetite the leach rate is higher, about 0.007 g.m1.d−2. The release rate to the solution of Cs is one order of magnitude lower and that of Pu-238 + Am-241 three orders of magnitude lower than the release rate of the soluble elements Mo and B. Most of the Pu-238 and Am-241 fraction, found in the solution, is present as colloids.